The GMC G3500 brake light component utilizes 1157 and 2057 bulb sizes depending on the specific production period for the vehicle. Available data covers the range from 1979 through 1996.
The year-by-year compatibility chart below provides a quick reference to verify the correct bulb size for your vehicle.
The GMC G3500 brake light uses the 2057 bulb for model years 1983-1996, while the 1157 bulb applies to model years 1979-1982.
Both the 2057 and 1157 are dual-filament bulbs sharing the BAY15d bayonet base, which means they are physically interchangeable in terms of socket fit.
Although the 2057 and 1157 share the same BAY15d base, their wattage ratings differ. The 2057 operates at 26.9W/8W while the 1157 operates at 21W/5W, making the 2057 the higher-output of the two on both filaments.
The dual-filament design of both the 2057 and 1157 serves two functions within a single housing, with the higher-wattage filament handling the stop light function and the lower-wattage filament handling the tail light function.
The Center High Mount Stop Light on the GMC G3500 uses the 921 bulb for model years 1988-1996.
The 921 is a single-filament wedge-type bulb in a T15 form factor, rated at 12V and 16W, and is not interchangeable with the BAY15d bayonet-base bulbs used in the standard brake light positions.
All three bulb types listed, the 2057, 1157, and 921, conform to ANSI standards recognized in both the United States and Canada.
The shift from the 1157 to the 2057 in the brake light position beginning with the 1983 model year represents a move to a higher-output filament specification within the same bayonet base format.